Krypton-fluorine bonds

The krypton atom in krypton difluoride does not obey the octet rule. The presence of five pair around the krypton leads to a trigonal bipyramidal electron-group geometry. The presence of three lone pairs and two bonding pairs around the krypton makes the molecule linear. The two krypton-fluorine bonds are polar covalent. However, in a linear molecule, the bond polarities pull directly against each other and cancel. Cancelled bond polarities make the molecule nonpolar. The strongest intermolecular force in the nonpolar krypton difluoride is London force. 

Following Bartlett s discovery of xenon hexafluoroplatinate(VI), xenon and fluorine were found to combine to give several volatile, essentially covalent fluorides, and at least one fluoride of krypton has been obtained. From the xenon fluorides, compounds containing xenon-oxygen bonds have been made much of the known chemistry of xenon is set out in Figure 12.1. 

The difference in the ionization potentials of xenon and krypton (1170 versus 1351 kj/mol) indicates that krypton should be the less the reactive of the two. Some indication of the difference can be seen from the bond energies, which are 133 kj/mol for the Xe-F bond but only 50 kj/mol for the Kr-F bond. As a result, XeF2 is considerably more stable of the difluorides, and KrF2 is much more reactive. Krypton difluoride has been prepared from the elements, but only at low temperature using electric discharge. When irradiated with ultraviolet light, a mixture of liquid krypton and fluorine reacts to produce KF2. As expected, radon difluoride can be obtained, but because all isotopes of radon undergo rapid decay, there is not much interest in the compound. In this survey of noble gas chemistry, the... 

The chemistry of krypton is considerably more extensive than that of argon nevertheless, it is stiU rather restricted. A series of krypton species containing Ki H, KiMI , and RtMI)l bonds were recently formed in low-temperature matrix isolation experiments by Rasanen and coworkers 10). The only hulk compounds of krypton that have been isolated are KrF2 (a very powerful fluorinating agent) and a series of cationic species derived from it, e.g., [KrF]+[SbF6] 11). All of these compoimds contain krypton in the +2 oxidation state. 

Fluorine (F) is one of the most reactive elements and forms chemical bonds with almost all the other elements (with the exception of helium and neon), though it takes higher temperatures to react with noble metals, such as gold, platinum, and palladium. Fluorine can even react with an inert gas (krypton) ... 

The product is a volatile, colorless solid (Figure 22.52). Since then, a number of noble-gas compounds have been prepared that typically involve bonds to the highly electronegative elements fluorine and oxygen. Most of these are compounds of xenon (see Table 22.12), but a few are compounds of krypton and radon. Recently, an argon compound, HArF, was synthesized as well as compounds of CUO bonded to Ne, Ar, Kr, and Xe. All of these recent compounds were synthesized at very low temperatures. 

In the past 40 years, other xenon compounds have been prepared— for example, Xe04 (explosive), Xe02F4, Xe02F2, and XeOsFj. These compounds contain discrete molecules with covalent bonds between the xenon and the other atoms. The structures of some of these xenon compounds are sununarized in Fig. 20.26. A few compounds of krypton, such as KrFj and KrF4, also have been observed. There is evidence that radon also reacts with fluorine, but the radioactivity of radon makes its chemistry very difficult to study. 

In 1988, G. J. Schrobilgen, professor of chemistry at McMaster University in Canada, reported the synthesis of an ionic compound, [HCN F] [AsFs], which consists of HCNKrF and Asp6 ions. In the HCNKTh" " ion, the krypton is covalently bonded to both fluorine and nitrogen. Draw Lewis structures for these ions, and estimate the bond angles. 

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